Method of preparing cell feed for the fused salt electrolytic production of titanium



WTHOD F PREPARING CELL FEED FOR THE FUSED SALT ELECTROLYTIC PRODUCTION0F TITANIUM Eugene Wainer, Cleveland Heights, Ohio, assignor, by

mesne assignments, to Horizons Titanium Corporatron, a corporation ofNew Jersey No Drawing. Original application November 8, 1954, Serial No.467,581, now Patent No. 2,868,703, dated January 13, 1959. Divided andthis application November 6, 1957, Serial No. 694,723

Claims. (CI. 75-10) This invention relates to a thermal method ofpreparing an alloy consisting principally of titanium with minor butdefinite proportions of carbon and oxygen, which is particularly usefulin the production of pure titanium.

Many methods have been proposed for theproduction of pure titanium metalwhich may be grouped generally as pyrometallurgical, chemical andelectrolytic. Each method suffers from serious disadvantages either asto the raw materials which are necessary, or the temperatures at whichthe desired reactions take place. Of the three approaches, theelectrolytic winning of titanium metal from various compounds appears toofier the simplest and most economical solution of the problem.

This application is a division of my copending application, filedNovember 8, 1954, Serial No. 467,581, which issued January 13, 1959, asUnited States Patent 2,868,703, disclosing and claiming the novelcomposition of matter adapted to serve as an improved cell feed materialfrom which titanium may be recovered electrolytically and which in turnwas a continuation-in-part of an earlier application Serial No. 320,113,filed November 12, 1952, which issued on November 1, 1955, as UnitedStates Patent 2,722,509.

In another of my copending applications Serial No. 398,192, filedDecember 14, 1953, and now abandoned, there is described a process inwhich titanium is deposited cathodically from a bath in which titaniumcarbide or mutual solid solutions of titanium carbide and titaniummonoxide are chlorinated in situ by suitable chlorinating agents.

In still another copending application Serial No. 398,193, filedDecember l4, 1953, by John T. Burwell, Jr., and Quentin H. McKenna, andissued as United States Patent 2,876,180 on March 3, 1959, a process isdisclosed wherein a transition metal is electrolytically deposited at acathode from a salt bath prepared by reacting in a fused halide. saltmedium, a transition metal carbide or solid solution of transition metalcarbide and monoxide such as' those of titanium with a transition metalhalide.

It is one object of this invention to provide an improved cell feedmaterial for processes such as those described. The cell feed materialmay, it will be noted, be a consumable anode, or a constituent of theelectrolytic bath, or a material employed in the preparation of thebath.

It is another object of the invention to provide a process for preparingthe novel cell feed material.

These and other objects are readily accomplished by bringing togethertitaniumcarbide and titanium monoxide under suitable reactionconditions. Inasmuch as titanium carbide and titanium monoxide have thesame cubic structure and spacegrouping and nearly the same lattice size,they are capable of forming a continuous series of solid solutionsranging from pure titanium carbide to pure titanium monoxide. intimatelymixed and subsequently heated to an appropriate elevated temperatureunder a reduced pressure, the

two components form a mutual solid solution from which,

When the individual components are 2,984,426 I Patented Sept. 15, 1959ice because of the reduced pressure, carbon monoxide tends to beeliminated.

The titanium carbide employed may be prepared by any of a number ofwell-known processes. It may be produced by reacting pure or pigmentgrade titanium dioxide (TiO in finely divided form (-325 mesh TylerStandard) with pure carbon (prepared by calcining lampblack) undercarefully controlled conditions so that the titanium dioxide issuccessively converted to T i 0 Ti O TiO and finally to TiC, thereaction at each of the stages taking place between solid materials. Theamount of carbon employed should be slightly in excess of thestoichiometric amount required for the complete conversion of TiO;, toTiC. The product obtained is substan-- tially pure TiC. If furtherpurification is desired the TiC may be crushed and any extraneousmaterials separated leaving a pure TiC suitable for reaction with thetitanium monoxide.

The titanium monoxide may be prepared in any known manner. It may beprepared from titanium carbide in the manner taught in each of US.Patents 2,681,847, 2,681,848, or 2,681,849. I prefer to follow thepractice described in United States Patent 2,750,259 wherein a processis disclosed in which titanium dioxide (TiO is converted first totitanium sesquioxide (Ti O and the sesquioxide is further reacted toproduce titanium monoxide (TiO).

In preparing both the titanium carbide and the titanium monoxide asabove described, it will be noted that the reactions occurred betweenmaterials in the solid state, and it will be further noted that thereare obtained relatively pure compounds of titanium and oxygen ortitanium and carbon by carrying out the reactions under carefullycontrolled conditions.

Although I presently prefer to use the pure carbide and the puremonoxide as starting materials for making the desired reaction mixture,the carbide and the monoxide may be somewhat impure without impairingthe effectiveness of the process constituting my invention. Thus thecarbide may contain some titanium oxide and the monoxide may containsome residual carbon or titanium carbide.

I have now found that titanium carbide and titanium monoxide may bereacted with one another to produce therefrom a product enriched intitanium content together with small amounts of carbon and oxygen.Essentially my method comprises melting titanium monoxide (TiO) in avacuum or partial vacuum and adding to the melt controlled amounts oftitanium carbide (TiC). By maintaining the temperature above theliquidus for the system Ti-TiO-TiC, and by removing carbon monoxide asrapidly as it is formed, a product enriched in titanium and impoverishedin both carbon and oxygen may be obtained. For instance, by addingtitanium carbide (which contains approximately 20% carbon) to moltentitanium monoxide (which contains about 25% oxygen) and removing thecarbon monoxide as it forms, a product containing in excess of 90%titanium may be obtained from starting materials with between andtitamum.

The foregoing reaction may be accomplished in many ways. In a preferredembodiment of the invention the TiC prepared as above indicated ismoistened with methylated spirit, shaped in the form of an electrode,and baked at a temperature of about 2100 C. for 4 hours.

. An electrode of TiO is similarly prepared at a temperature of 1700 C.An arc is struck between an electrode of titanium carbide and anelectrode of titanium monoxide under partial vacuum and the moltendrippings are collected while the evolved carbon monoxide is removed byactive vacuum pumping.

As a second embodiment, pellets may be prepared from a mixture oftitanium carbide and titanium monoxide proportioned so as to produce thedesired final Ti-OC composition. The pellets may then be fed into thehearth of a water-cooled tungsten are, water-cooledcopper hearth arcmelting furnace and melted thereon under an actively pumped vacuum toremove carbon monoxide gas generated during the process.

As a further alternatlive, consumable electrodes may be are melted toproduce the desired alloy. Thus a powdered mixture of titanium carbideand titanium monoxide proportioned as above may be moistened withmethylated spirits and then pressed or extruded into the form of pencilssuitable for use as electrodes and then baked or partially sintered. Therods so obtained have an excellent conductivity and may be used asconsumable electrodes in an arc-melting furnace from which carbonmonoxide may be removed continuously, as rapidly as it is evolved. I

The novel titanium, carbon and oxygen products of this invention arereadily formed by bringing together at temperatures above the meltingpoint of TiO (1750 C.) pure titanium carbide and pure titanium monoxide1n suitable proportions, consistent with the temperature and pressure ofoperation to yield the described alpha titanium alloy with oxygen andcarbon containing a small amount of a second phase, presumably TiC.While I do not wish to be bound by any specific theory as to whatoccurs, one possible explanation for the reaction may be oifered basedon the phase diagrams for three binary systems Ti-TiO, Ti-TiC, andTiOTiC, and the melting points for the ternary system TiOC representedas Ti-TiO-TiC.

Starting with a mixture of TiO and TiC in equimolar proportions in anarc furnace, as the temperature is raised, the TiO melts at 1750 C. andTiC gradually dissolves in the TiO as shown by the liquidus line of theT iO-TiC quasi-binary. Carbon monoxide is formed by the reaction betweenTiO and TiC and is removed by the vacuum pump, changing the over-allcomposition toward the titanium cor er of the ternary diagram. As thecomposition is progressively depleted in carbon and oxygen andcorrespondingly enriched in titanium, the melting point graduallyfollows the liquidus-surfaces in the ternary diagram. When suflicientcarbon monoxide has been removed, the oxygen content of the system islowered to such an extent that the over-all composition falls within thealpha region of the TiTiO binary. In equilibrium at this time are 1)alpha titanium, saturated with oxygen, and (2) titanium carbide. Furtherremoval of carbon monoxide through the active vacuum pumping permits theoxygen content to be further lowered to a value determined by thetemperature, pressure, and carbon content. Eventually an alloy oftitanium is produced consisting of alpha titanium saturated with oxygenas one phase and gamma TiO C as a second phase. In the specific instancecited, i.e., starting with a mol-mo-l mixture of TiO and TiC analyzing12.9% 0, 9.7% C and 77.4% Ti (all weight percents), I have obtained analloy analyzing 5.2% O, 5.5% C and 89.1% Ti by weight. In the system,this would represent an alloy of alpha titanium saturated with respectto oxygen and carbon whose total weight is equal to 97.7% of thecomposition, the remaining 2.3% being free titanium carbide.

In general, the products obtainable by my process have been found byanalysis to contain from 89% to 92% titanium, from 2.5% to 5.5% carbon,and from 1.5% to 5.5% oxygen, depending on the temperature at which themolten mass was held, the proportions of TiC and TiC employed, thedegree of vacuum, and the length of time the molten mass was held attemperature.

The following additional examples will serve to further illustrate myinvention:

Example I Titanium carbide of 325 mesh particle size (Tyler Standard)analyzing 78.1% Ti and 21.7% C, and TiO of -325 mesh particle size(Tyler Standard) analyzing 73.3% titanium, 2.2% carbon and 24.0% oxygen,were blended in equimolar proportions, based on stoichiometriccombination of available carbon and oxygen. The mixture was pressed intoa 20 gram pellet at 20 tons per square inch without the use of a binder.

The pellet was fused in the electric arc in an atmosphere of 15 inches(mercury) or argon. Reaction was continued until fuming stopped and thecharge had c0- alesced into a round button.

The button, when cooled, was silvery in color. Chemical analysisindicated titanium and carbon content of 89.5% and 5.9% respectively.Vacuum fusion analysis indicated an oxygen content of 4.4%.

Example II Titanium carbide of 325 mesh particle size (Tyler Standard)analyzing 78.1% titanium and 21.7% carbon, and titanium monoxide of'-325 mesh particle size (Tyler Standard) analyzing 73.3% titanium, 2.3%car'- bon, and 24.0% oxygen, were blended in a proportion calculated toprovide an excess of 1.5 weight percent carbon over the amount of carbonrequired to combine stoichiometrically with the oxygen.

The material was pelleted and fused as in the preceding example.Chemical analysis indicated titanium and carbon contents of 91.6% and4.7% respectively. Vacuum fusion analysis indicated an oxygen content of3.4%.

The high titanium alloys of this invention containing oxygen and carbonare distinguished from other prior art titanium-oxygen-carbon compoundsby their extremely high titanium content. For example, Kinz'ie and Hokein US. Patent 2,040,854 reported a product correspondingto the formulaTi OC with a titanium content between 67% and 69%, While in US. Patent2,129,161, Kinzie and Wainer describe a substance containing about 65.5%Ti corresponding to Ti OC Other substances such as TiOC containing 63.3%Ti and Ti OC containing 77.4% Ti are also known, but none of these priorart materials is as rich in titanium as the product of my process whichis hexagonal close packed titanium containing some oxygen and carbon asthe major phase, with a small amount of titanium carbide as the minorphase.

By virtue of its high titanium content, my product is peculiarly adaptedto be employed as the cell feed material in an electrolytic process forthe production of titanium. As a cell feed material it may findapplication in any one of several ways. For example, an anode formed ofthe titanium-oxygen-carbon product of this invention may be caused togive up its titanium which is transported through the fused bath to thecathode where it is deposited, in accordance with the process describedand claimed in my application Serial No. 320,113, which issued onNovember 1, 1955, as Patent 2,722,509. As another alternative, thetitanium-oxygen-carbon product of my invention may be added to a fusedhalide salt bath and reacted therein with chlorine to produce a bathwhich on electrolysis yields a deposit of titanium at the cathode, inaccordance with the continuous process described and claimed in mycopending application Serial No. 398,192. Other uses will readilysuggest themselves to those skilled in the art, it being obvious thatthe product of this invention may be used as a starting material for thepreparation of titanium compounds as well as for the electrolyticrecovery of titanium.

I claim:

l. A method of preparing a cell feed material suitable for theelectrolytic recovery of titanium'and containing between 89% and 92%titanium by weight comprising: melting titanium monoxide, addingtitanium carbide to the melt, maintaining the resultingcompositionevolved from the melt, continuing the addition of titaniumcarbide and the removal of carbon monoxide until the melt has beenenriched to a titanium content between 89% and 92%, and recovering theso enriched titanium product.

2. The method of claim 1 in which the titanium monoxide is melted undera reduced pressure.

3. A method of preparing a cell feed material suitable for theelectrolytic recovery of titanium and containing between 89% and 92%titanium by weight comprising preparing a mixture of finely dividedtitanium monoxide and finely divided titanium carbide, proportioned tocontain between about 75% and 80% titanium, as monoxide and carbide, byweight, pelleting the said mixture, melting the pellets in an inertatmosphere in an arc furnace, maintaining an inert atmosphere in saidfurnace and maintaining a pressure of less than one atmosphere in saidfurnace, removing carbon monoxide as it is evolved from the melt,maintaining the melt molten until the resultant product is enriched to atitanium content of between 89% and 92%, by weight, and depleted incarbon and oxygen and recovering the so prepared product.

4. A method of preparing a cell feed material suitable for theelectrolytic recovery of titanium and containing between 89% and 92%titanium by weight comprising 25 preparing a mixture of finely dividedtitanium monoxide and finely divided titanium carbide, proportioned tocontain between about 7 5% and 80% titanium, as monoxide and carbide, byweight, shaping the mixture into the form of electrodes, consuming theelectrodes in an arc furnace as consumable electrodes, maintaining aninert atmosphere in said furnace and maintaining a pressure of less thanone atmosphere in said furnace, removing the carbon monoxide as it isevolved during the consumption of the electrodes, and recovering theproduct.

5. A method of preparing a cell feed material suitable for theelectrolytic recovery of titanium and containing between 89% and 92%titanium by Weight comprising preparing an electrode of titaniumcarbide, preparing an electrode of titanium monoxide, striking an arebetween the said electrodes and collecting the molten product thereofwhile continuously removing any carbon monoxide evolved during thearcing and melting, maintaining the molten product under an inertatmosphere having a partial pressure of carbon monoxide less than oneatmosphere and recovering the resultant product depleted in carbon andoxygen and containing between 89% and 92% by weight of of titanium.

References Cited in the file of this patent UNITED STATES PATENTS1,523,103 DAdrian Ian. 13, 1925 2,205,386 Balke et al. Jan. 25, 1940FOREIGN PATENTS 754,981 Great Britain Aug. 15, 1956

1. A METHOD OF PREPARING A CELL FEED MATERIAL SUITABLE FOR THEELECTROLYTIC RECOVERY OF TITANIUM AND CONTAINING BETWEEN 89% AND 92%TITANIUM BY WEIGHT COMPRISING: MELTING TITANIUM MONOXIDE, ADDINGTITANIUM CARBIDE TO THE MELT, MAINTAINING THE RESULTING COMPOSITIONUNDER AN INERT ATMOSPHERE AND UNDER A PRESSURE OF LESS THAN ONEATMOSPHERE, MAINTAINING THE MONOXIDE MOLTEN WHILE CONTINUOUSLY REMOVINGTHE CARBON MONOXIDE EVOLVED FROM THE MELT, CONTINUING THE ADDITION OFTITANIUM CARBIDE AND THE REMOVAL OF CARBON MONOXIDE UNTIL THE MELT HASBEEN ENRICHED TO A TITANIUM CONTENT BETWEEN 89% AND 92%, AND RECOVERINGTHE SO ENRICHED TITANIUM PRODUCT.